It says they can "learn and cast spells on the cleric spell list", for wizards learning a spell involves writing it into your spellbook, so that's not a correct reading. There's literally 0 reading I can see that would prevent a duskblade from benefitting from from it as well. Ask your DM why wizards gain the benefit but duskblades do not? Ask him if a sorcerer would benefit? If a sorcerer would, then duskblades 100% should, since they practically learn and cast spells as sorcerers do.